Functional dependency

Updated April 02, A functional dependency in a database enforces a set of constraints between attributes.

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Functional dependency example, by A. Since the values of A are unique a1, a2, a3, etc.

Trivial functional dependency

Equation for axiom of augmentation. This occurs when one attribute in a relation uniquely determines another attribute. Functional dependency example, by A. Figure We might have a table Employee with attributes employee, title, department, location and manager. Here are a few examples. Continue Reading. This must also work for a composite PK. Given SIN, we can determine any of the other attributes within the table. For any relation R, attribute Y is functionally dependent on attribute X usually the PK , if for every valid instance of X, that value of X uniquely determines the value of Y. For example, if:. Looking at actual data can help clarify which attributes are dependent and which are determinants. The left side of a functional dependency can include more than one attribute. Table

Without normalization, there is no assurance that the data in a database is accurate and dependable. As you look at this table, ask yourself: What kind of dependencies can we observe among the attributes in Table R?

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Equation for axiom of transitivity. Here are a few examples. The attribute SSN will determine the value of name, date of birth, address and perhaps other values, because a social security number is unique, while a name, date of birth or address may not be.

The table below has information not directly related to the student; for instance, ProgramID and ProgramName should have a table of its own.

functional dependency in dbms pdf

Put another, more concrete way, if we know the value of the SSN attribute, we can find the value of name, date of birth and address.

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Functional Dependency in DBMS